UNIVERSITY    OF   CALIFORNIA        AGRICULTURAL    EXPERIMENT    STATION 
COLLEGE    OF   AGRICULTURE  benj.  ide  wheeler,  president 

THOMAS    FORSYTH    HUNT,  Dean  and  Director 

BERKELEY  h.  e.  van  norman,  vice-director  and  dean 

University    Farm    School 

CIRCULAR  No.  116 

(March,  1914) 


SILK  WORM  EXPERIMENTS 

BY 
C.  W.  WOODWORTH 


The  Agricultural  Experiment  Station  will  send  a  small  quantity 
of  silkworm  eggs  free  of  charge  to  any  one  willing  to  co-operate  with 
it  in  its  effort  to  make  silk  culture  profitable  in  California. 

A  large  number  of  eggs  of  all  the  leading  races  of  silkworms  from 
various  countries  where  the  silk  is  grown  commercially,  in  Europe  and 
Asia,  have  been  secured  and  we  desire  to  interest  as  large  a  number 
of  persons  as  possible. 

Thus  far  the  growing  of  silk  has  been  unprofitable  in  this  state. 
The  reason  it  has  not  developed  here  is  strictly  because  of  our  economic 
conditions.  The  climate  in  many  parts  of  the  state  is  ideal  and  silk- 
worms have  been  grown  here  every  year  in  small  quantities  for  more 
than  a  generation.  As  long  as  the  profits  from  other  industries  are 
larger  than  those  secured  in  growing  silk,  this  industry  cannot  thrive 
and  should  not  be  encouraged. 

Neither  the  price  of  silk  nor  the  cost  of  labor  are  liable  to  change 
enough  in  the  near  future  to  render  the  growing  of  silk  profitable  in 
this  state  if  carried  on  in  the  usual  manner. 

The  present  experiment. — There  is,  however,  a  possibility  that  the 
cost  of  production  can  be  diminished  as  has  been  done  in  recent  years 
in  the  case  of  many  other  agricultural  crops.  The  use  of  a  cheaper 
food,  or  the  employment  of  less  expensive  methods  of  handling  the 
worms,  may,  either  of  them,  be  sufficient  to  place  the  industry  on  a 
sound  financial  basis. 

We  are  soliciting  co-operation  in  the  attempt  to  solve  the  first  of 
these  problems,  the  securing  of  cheaper  food,  by  testing  as  great  a 
range  of  food  plants  as  possible.  We  propose  to  endeavor  to  develop 
silkworms  that  will  thrive  on  some  plant  producing  more  tons  of  leaves 
to  the  acre  and  one  cheaper  to  harvest  than  the  mulberry,  which  has 
hitherto  been  exclusively  employed  in  silk  production. 


The  production  of  such  a  race  will  require  the  breeding  together 
of  individuals  that  have  less  strongly  developed  the  natural  repug- 
nance to  other  kinds  of  foliage  until,  finally,  if  successful,  a  breed  is 
evolved  which  will  thrive  upon  some  satisfactory  forage  crop. 

We  have  secured  as  great  a  variety  of  races  of  silkworms  as  we 
could,  and  will  test  as  large  a  variety  of  plants  as  possible,  so  as  to 
have  a  great  abundance  of  individuals  with  diverse  food  reactions 
from  which  to  select  in  making  our  matings.  The  greater  this  variety 
(and  if  many  co-operate  this  can  be  very  large)  the  more  probable  it 
would  seem  that  satisfactory  races  would  arise. 

How  to  conduct  the  experiment. — The  care  of  silkworms  is  a  very 
simple  process  that  anyone  can  perform;  indeed,  in  most  countries  a 
large  proportion  of  the  work  is  done  by  children.  When  only  a  few 
are  kept  together,  practically  all  the  directions  that  are  necessary  is 
that  they  be  kept  supplied  with  fresh  food,  and  that  which  is  not 
eaten  be  removed  if  it  does  not  dry  up  completely,  since  the  litter 
should  not  be  permitted  to  become  moldy. 

The  testing  of  various  food  plants  consists  simply  in  offering  them 
a  meal  of  one  kind  of  leaf  and  then  another,  but  alternating  with 
mulberry  or  other  known  food  plant  so  that  the  worms  will  not  suffer 
for  lack  of  food,  and  finally  when  something  is  found  that  they  will 
relish  they  may  be  limited  to  that  food  and  reared  to  maturity  upon  it. 

While  the  mulberry  is  the  only  leaf  used  in  Europe  and  Asia  for 
the  production  of  silk,  osage  orange  has  been  similarly  employed  in 
the  Mississippi  Valley  on  a  small  scale,  producing  silk  equal  in  every 
respect  to  that  grown  on  mulberry,  and  silkworms  have  often  been 
fed  on  lettuce  for  a  portion  or  even  the  whole  of  their  lives.  More 
than  a  hundred  years  ago  English  investigators  had  succeeded  in 
rearing  them  on  quite  a  variety  of  plants,  including  blackberry,  elm, 
sweet  cowslip,  primrose,  spinach,  and  viper  grass. 

There  is  much  difference  in  their  acceptance  of  lettuce  as  a  food, 
as  shown  by  different  races.  We  have  already  this  year  had  worms 
of  three  races  starve,  while  those  of  two  other  races  eat  this  leaf 
greedily,  and  we  have  had  similar  experiences  in  other  years.  Tem- 
perature has  been  observed  to  have  great  influence,  caterpillars  accept- 
ing unusual  food  much  more  readily  when  they  are  kept  in  a  warm 
room.  The  condition  of  the  leaf  also  has  an  effect,  the  young  and 
tender  leaves  being  more  freely  eaten.  The  age  of  the  insect  makes  a 
striking  difference,  the  older  insect  becoming  less  particular  as  to  the 
character  of  the  food.  All  of  these  facts  may  be  of  importance  in 
our  task  of  overcoming  the  present  natural  instinct  of  this  insect. 


Those  who  accept  the  eggs  will  be  expected  to  do  the  following : 

( 1 )  Endeavor  to  feed  the  worms  on  some  other  kind  of  leaves  than 
mulberry. 

(2)  Keep  a  record  of  the  foods  tried. 

(3)  Return  to  us,  say,  half  of  the  cocoons  as  soon  as  spun,  together 
with  a  record  of  their  feeding,  so  that  we  can  use  the  moths  produced 
in  our  breeding  experiments. 

After  these  lay,  we  will  be  glad  to  return  to  those  co-operating 
with  us  a  larger  quantity  of  eggs  for  their  next  season's  rearing  from 
these  especially  selected  moths. 

How  to  obtain  the  eggs. — Send  a  card  addressed  to  Professor  C.  W. 
Woodworth,  University  of  California,  Berkeley,  CaL,  asking  that  eggs 
be  reserved  for  you,  giving  your  postoffice  address. 

The  eggs  are  now  held  in  cold  storage  and  will  not  be  shipped 
until  the  mulberries  come  into  leaf,  but  the  sending  of  a  card  at  this 
time  will  insure  that  eggs  will  be  reserved  for  you. 

Ordinarily  only  a  single  lot  of  about  a  hundred  eggs  will  be  sent 
to  one  address;  however,  anyone  who  is  prepared  to  co-operate  on  a 
larger  scale  may  receive  more  than  one  lot.  Teachers  may  arrange, 
for  instance,  for  a  lot  for  each  pupil  by  agreeing  to  take  general 
charge  of  the  whole  set  of  experiments  and  to  see  that  the  cocoons  are 
promptly  sent  in  for  our  breeding  work. 

Feeding  the  worms — The  usual  practice  is  to  give  the  worms 
chopped  leaves  during  the  first  two  stages,  and  whole  leaves  the  rest 
of  their  life.  The  number  of  meals  a  day  and  the  rations  at  each  meal, 
of  course,  will  vary  to  some  slight  extent  according  to  the  needs  of 
the  worms.  When  it  is  warmer  they  may  require  more  food,  and  when 
it  is  cooler  less.  The  optimum  temperature  is  usually  placed  at  72 
degrees  Fahrenheit.  If  the  temperature  is  a  little  higher,  they  may 
come  to  maturity  a  little  more  quickly,  and  if  it  is  lower,  they  will 
take  distinctly  longer  to  mature. 

Care  of  the  worms. — Silkworms  are  very  subject  to  disease,  espec- 
ially when  grown  in  large  numbers,  and  to  prevent  this  the  silk-raisers 
must  exercise  the  utmost  care,  particularly  in  the  removal  of  the 
droppings  of  the  worms  and  of  the  uneaten  remains  of  the  food. 
Neglect  in  these  matters  usually  results  in  the  starting  of  an  epidemic 
among  the  worms,  showing  itself  at  each  molt,  but  most  fatally  just 
as  the  worms  are  about  ready  to  spin.  If  the  conditions  are  not 
maintained  absolutely  sanitary  'it  is  not  infrequent  to  lose  from  50  to 
75  per  cent  of  the  worms  just  as  they  are  about  to  undertake  their 
labors  of  silk  production.     There  are  quite  a  number  of  silkworm 


diseases  recognized  by  silk-growers,  some  of  which  are  hereditary,  and 
may  destroy  the  worms  in  spite  of  the  best  of  care.  Very  commonly 
the  loss  with  amateurs,  however,  is  entirely  preventable,  and  represents 
simply  the  carelessness  of  the  grower.  The  means  of  cleaning  the 
trays  used  for  silkworms  is  the  use  of  mosquito  net  during  the  first 
two  stages,  and  a  coarse  string  net  when  the  insects  are  larger;  or 
perforated  paper  has  proven  very  satisfactory  where  it  can  be  ob- 
tained. The  net  is  laid  over  the  worms  just  before  feeding,  and  they 
will  crawl  through,  leaving  the  old  leaves,  which  can  then  be  removed. 
It  is  a  good  plan  to  change  them  at  least  once  a  day,  and  if  the  weather 
is  moist  the  use  of  disinfectants  in  the  room  and  about  the  trays  is 
certainly  to  be  approved.  The  nets  used  in  changing  the  food  should 
be,  under  any  condition,  treated  from  time  to  time  with  antiseptics. 
Good  ventilation  should  be  provided  to  decrease  the  liability  of  ex- 
cessive moisture,  which  is  one  of  the  conditions  under  which  diseases 
most  readily  develop. 

Spinning. — When  the  insects  are  fully  fed  they  begin  to  wander 
about,  cease  to  feed,  and  become  much  more  transparent  in  appearance. 
These  are  indications  of  the  approach  of  the  spinning  time.  They 
must  now  be  provided  with  places  for  spinning  their  cocoons.  The 
practice  in  Europe  is  to  furnish  them  with  brush  cut  in  the  winter 
from  trees  and  bound  together  in  such  a  way  that  they  may  be  set 
upon  the  trays  in  rows,  spreading  out  hedgelike  at  the  top.  The 
worms  climb  up  into  these  hedges  and  spin  their  cocoons  between  the 
twigs.  A  very  satisfactory  arrangement  can  be  made  of  lath  by 
laying  them  edgewise  about  three-fourths  of  an  inch  apart  and  tacking 
other  laths  at  right  angles  across  these  to  hold  them  in  position. 


